Not applicable
No applicable
The present invention relates to rotary gear pumps and motors in general, and to the type having pressure balanced bearing block seals in particular.
So-called external gear pumps are used in hydraulic power applications, as both motors and pumps. Reasonable efficiency, long life, and low-cost are normally the design criteria for these widely used pumps and motors. An external gear pump has a pair of intermeshing gears. The gears incorporate shafts which are parallel and which are mounted in bearing blocks which seal the ends of the gears. The gears are contained within a housing and hydraulic oil is supplied at an inlet and is pumped to an outlet on the other side of the meshing gears.
External gear pumps or motors, when used in hydraulic power applications, operate with pressures of up to several thousand pounds per square inch (psi). The high differential pressure and the importance of efficiency makes pump slip a concern. Slip is the fluid flow which leaks from the high-pressure side of the pump or motor to the low-pressure side. The design of external gear pumps minimizes pump slip by careful attention to pump design details. One major source of pump slip is the seal between the end faces of the rotors/gears and opposed bearing blocks. The opposed bearing blocks contain the bearings into which the shafts on which the gears are mounted turn.
The bearing blocks are positioned above and below the rotors in a twin lobe passageway formed in the motor housing. Oil pressure is allowed to reach the distal sides of the bearing blocks, forcing them toward the end faces of the rotors. However, the bearing blocks necessarily must be supported with uneven pressure so as to match the pressure developed within the pump as the rotors turn to carrying fluid from the low-pressure side of the pump to the high-pressure side. If the pressure on the sides of the bearing blocks opposed to the end faces of the rotor are not adequately matched to the pressures developed between the gear teeth of the pump, excessive slippage or bearing block face wear will result. Proper balancing of pressure on the side of the bearing blocks opposite to the end faces of the rotor is typically accomplished by a sealing gasket which supplies different pressures to different portions of the bearing blocks.
The tooling costs for the fabrication of bearing blocks is high, as the finish and dimensions of the block require tight tolerances. Thus, a single block design is often used in several different pump designs. Typically a family of hydraulic pumps will be designed to accommodate a range of hydraulic fluid inlet sizes. The inlet size of the hydraulic pump causes a variation in the hydraulic loading on the bearing blocks. Therefore, the design of the sealing gasket has to the present time been a compromise.
What is needed is a family of external hydraulic gear pumps which can accommodate a variety of hydraulic fluid inlets with a single bearing block design which has better bearing block sealing and reduced bearing block face wear.
The external hydraulic gear pump of this invention incorporates a chamfer in the bearing blocks on either side of the hydraulic fluid inlet. The chamfer functions to cause a family of pump designs with varying hydraulic inlet sizes, to have similar bearing block pressure profiles. The chamfer prevents the buildup of hydraulic pressure immediately adjacent to the hydraulic inlet below a given inlet size so that the bearing block pressure profile for a family of pumps with different inlet sizes more nearly matches the pressure profile of the largest opening used in a particular design family. The sealing gasket on the side of the bearing block opposite the gears is designed to accommodate this single pressure profile. The result is an improved bearing life and reduced slippage, over an entire family of pumps and motors of similar design.
It is an object of the present invention to reduce the cost of producing a family of hydraulic pumps or motors.
It is another object of the present invention to provide a family of hydraulic pumps or motors wherein the needed hydraulic sealing pressure remains substantially constant over a range of hydraulic fluid inlet sizes.
It is a further object of the present invention to provide a family of hydraulic pumps or motors with reduced wear.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.